1. Field of the Invention
The present invention relates to electrochemical processes for removing excess metal by electrolytic dissolution, effected by a counter electrode acting as the cathode against an electrode acting as the anode and, more particularly, to an electrochemical process using current density controlling techniques, designed to electrochemically machine electrodes while controlling the amount of an applied electric current, thus effectively producing a precise product having a uniform shape in addition to precise products having a variety of shapes.
2. Description of the Prior Art
As well known to those skilled in the art, an electrochemical process, also known as an electrolytic process, means a process, in which an electrode in an electrolyte is electrochemically reacted in response to applied voltages to be dissolved into the electrolyte. Such an electrochemical process is typically carried out in four steps as follows.
That is, the conventional electrochemical process comprises the first step of transferring the ions of the electrolyte to the surface of an electrode, the second step of reacting the metal atoms of the surface of the electrode with the transferred ions of the electrolyte to form particles, the third step of changing the particles into stable ions, and the fourth step of diffusing the stable ions into the electrolyte.
Such electrochemical processes are also classified as electrochemical polishing and electrochemical etching in accordance with results from a comparison of the processing rate of the second step with the processing rate of the third step. That is, the first processing rate when the metal atoms of the surface of the electrode are reacted with the transferred ions of the electrolyte to form, particles in the second step and the second processing rate when the particles are changed into stable ions in the third step are primarily measured prior to comparing the two processing rates with each other. When the first processing rate is higher than the second processing rate, the electrochemical process is an electrochemical polishing. When the first processing rate is lower than the second processing rate, the electrochemical process is an electrochemical etching. During such electrochemical processes, the difference between the processing rates in the above-mentioned four steps is an important factor that determines the surface conditions of the electrode in addition to the machined shape of the electrode. On the other hand, the metal dissolution rate in an electrochemical process is determined by the fourth step of diffusing the stable ions into the electrolyte.
Of the conventional electrochemical processes, the electrochemical etching is used specifically for machining micro probes having a precision of several nanometers. The electrochemical etching for machining such micro probes is typically performed with somewhat low concentrations of electrolytes and electric current. During an electrochemical etching for machining a micro probe, the metal dissolution rate is higher at the tip of the probe having a large curvature than the sidewall of said probe, thus making the tip have an unwanted conical shape. Such an effect of undesireably forming the conical tip during an electrochemical etching is a so-called xe2x80x9cgeometric effectxe2x80x9d in the art.
However, such conventional electrochemical etching has the following problems.
That is, the processing conditions for an electrode during an electrochemical etching are different in accordance with the depths of the parts of said electrode within an electrolyte, and so the metal dissolution rate of the electrode is partially uneven. It is thus almost impossible for the conventional electrochemical etching to produce a precise product having a uniform shape. Another problem experienced in the conventional electrochemical etching resides in that it is almost impossible to produce precise products having a variety of shapes due to the nonuniform metal dissolution rates.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an electrochemical process using current density controlling techniques, which electrochemically machines an electrode while controlling the amount of an applied electric current, thus effectively producing a precise product having a uniform shape.
Another object of the present invention is to provide an electrochemical process using current density controlling techniques, which electrochemically machines electrodes while controlling the amount of an applied electric current, thus producing precise products having a variety of shapes.
In order to accomplish the above object, the present invention provides an electrochemical process using current density controlling techniques, comprising: a contact point measuring step of sinking a cathode rod activated with a negative voltage into an electrolyte within a container, and feeding a cylindrical electrode having a predetermined length and activated with a positive voltage to the surface of the electrolyte until the electrode comes into contact with the electrolyte while measuring a contact point, at which an electric current initially flows into the electrolyte; an etching preparing step of feeding the electrode to the surface of the electrolyte and removing the applied voltage from the electrode, and sinking the electrode in the electrolyte by a length, which is predetermined on the basis of the contact point and to which the electrode has to be machined; an initial value setting step of setting a target length of the electrode, a target diameter of the electrode, an electrochemical equivalent volume constant of the electrode, a current density, and etching intervals; [a] an etching step of applying voltages to both the electrode and the cathode rod to electrochemically machine the electrode while continuously calculating and measuring a variable surface area of the electrode, the amount of applied current, the amount of electricity according to the applied current, and a variable diameter of the electrode in accordance with the lapse in etching time; and a process-end determining step of determining whether the diameter of the machined electrode from the etching step is equal to the target diameter, thus repeating the etching step until the target diameter of the electrode is accomplished or stopping the etching step when the target diameter of the electrode is accomplished.
In the above-mentioned electrochemical process, the variable surface area of the electrode during the electrode etching step is calculated by the expression, Am=xcfx80[LD+h(Do+2D)/3], wherein Am is the variable surface area (mm2) of the electrode during etching, L is a target length (mm) of the electrode, h is an additional increase (mm) of the contact position of the electrolyte surface, D is the variable diameter (mm) of the electrode during etching, and Do is an original diameter (mm) of the electrode.
In addition, the amount of applied current during the etching step is calculated by the expression, i=AmJ, wherein i is the applied current (C/sec) during a unit of time, Am is the variable surface area (mm2) of the electrode during etching, and J is the current density (C/mm2sec).
The amount of electricity during the etching step is calculated by the expression, Qt=Qp+ixcex94t, wherein Qt is the total amount of applied electricity (C) during etching, Qp is the amount of electricity (C) applied during the previous step, and xcex94t is a variable etching time (sec).
In addition, the variable diameter of the electrode during the etching step is calculated by the expression, xcfx80(Doxe2x88x92D)[L(Do+D)/4+h(3Do+2D)/15]xcex1e=Qt, wherein D is the variable diameter (mm) of the electrode during etching, Do is the original diameter (mm) of the electrode, Qt is the total amount of applied electricity (C) during etching, L is the target length (mm) of the electrode, h is the contact length (mm) of the electrode due to the surface tension, and xcex1e is the electrochemical equivalent volume constant (mm3/C) of the electrode.
In the electrochemical process of this invention, both the metal ion dissolving rate and the metal ion diffusing rate of the electrode are controlled by controlling the amount of the applied current.
In addition, the cathode rod may be somewhat freely selected from a variety of conductive rods, but it is preferable to use a carbon rod as the cathode rod.
The electrolyte may be selected from a variety of conventional acid solutions or basic solutions, which have been typically used in such electrochemical processes. But, it is preferred to use a potassium hydroxide solution having a molar density of 4xcx9c6 M as the electrolyte in the etching process of this invention.
In the electrochemical process, the electrode is ultrasonically washed on its surface with both acetone and distilled water before the contact point measuring step so as to remove impurities from the surface of the electrode.
On the other hand, the additionally machined volume of metal of the electrode due to the surface tension in the electrochemical process is calculated by the expression, Vp=xcfx80h(xe2x88x922D2xe2x88x92DoD+3D02)/15, wherein Vp is the additionally machined volume (mm3) of metal of the electrode due to the surface tension, h is the contact length (mm) of the electrode due to the surface tension, D is the variable diameter (mm) of the electrode during etching, and Do is the original diameter (mm) of the electrode.